1. Field of the Invention
The invention relates to a practical and successful procedure for manufacturing sheet metal preferably aluminum, can end structures for food product cans which may be opened easily by tearing a portion of the can end along a score line formed in the end member wherein the cans and can ends may be of the general types shown in Henning et al Pat. No. 3,490,643 and in Bernard J. McKernan application Ser. No. 70,843 filed Sept. 9, 1970, and wherein the can end structures have a hazard-eliminating protective triple metal thickness dull edge fold formation on the end panel removed from the can end structure when torn therefrom.
2. Description of the Prior Art
A number of can designs have been supplied to and used by food packers for packaging small quantities of snack foods such as puddings for children's lunch boxes. These cans have been made of aluminum and have had full opening container ends, the end panels of which are torn out using pull-rings attached to the can end panels.
Problems have been encountered in the use of such cans. Zipping off the lid or removable end panel in the can wall is not always easy for children; all to frequently they cut their fingers on the sharp lid edge or on the rim left inside the can, and the lid almost never comes off without a thick coating of pudding sticking to its underside. The child tempted to lick the lid stands a good chance of cutting his tongue on the sharp edge. The removed lid has been found to be sharp enough to slice a chicken leg.
A report by a school teacher about cut tongues suggested that the can design should be changed to eliminate the hazard, and suggested that this would be easier than attempting to change the natural tendencies of a child to lick pudding sticking to the underside of a removed lid. One trade journal has described the cans as dangerous and has questioned whether the convenience of the cans is worth their hazard.
As a result, food packers that have used such cans have called for a solution to the problem which will eliminate the dangers and hazards.
The can end structure shown in said application Ser. No. 229,678 satisfies this need. However, there have been substantial difficulties encountered in providing for the manufacture of such can end structures. These difficulties involve a number of factors. First, the thinness of and variations in the thickness of the aluminum sheet material, used to permit tearing out of an end panel along a score line, renders cold working operations to form a fold of triple thickness extending annularly around a recessed panel portion in the can end member and with the three layers of the fold extending generally parallel with the plane of the sheet aluminum panel portion extremely difficult to perform without tearing the blank metal, or thinning it to such an extent as to weaken the can end beyond required limits.
Next, the location of the triple fold in a recessed panel, initially drawn in a metal blank, offset from a terminal annular bead flange provided on the can end structure for subsequent seaming at a cannery to a can body, in an annular zone very close to a recessed corner defining the panel recess, and with a continuous generally circular score line located intermediate the fold and corner at a required location with respect to the fold, may promote thinning of the metal in the blank at various stages in the metal working procedures to an unacceptable degree or in an uncontrollable manner.
Further, the formation of a rivet integrally in the blank the riveting thereof to mount a pull ring on the panel portion to be torn from the can end, and the location of the rivet in the can end close to the zone of the can end where the score line is initially ruptured by the pull ring, all add to the complications encountered in attempts to provide practical, satisfactory, successful and readily controlled procedures or series of cold working operations which are repeatable under high speed production conditions to fabricate can end products which meet the required specifications for the stated folded can end structure. In addition, the stiffness of the prior application three layer fold renders the initial severing of the score line difficult in opening the can to remove the panel portion.
These considerations, and the difficulties encountered in attempting to eliminate the complications and to solve the problems that have arisen, thus have presented a need for effective, satisfactory and efficient procedures for the manfacture of folded sheet metal can ends, and for a folded can end in which the folded zone is easy to bend when initially rupturing the score line.